1. Field of the Invention
The present invention relates to a purification method of a crude product by column chromatography, in which methanol-containing n-hexane and/or n-hexane-containing methanol is used as an eluent.
2. Description of the Background Art
A great number of methods have heretofore been applied to purification of crude products. Among these, column chromatography excellent in separation efficiency has been often used.
In column chromatography on silica gel (hereinafter may be referred to as "silica gel column"), a crude product mixture consisting of a plurality of components is caused to be adsorbed on silica gel as a solid support, stationary state, and the components are then separated and purified making good use of differences between the components in adsorption coefficient and partition coefficient to the stationary phase and a mobile phase generally by successively varying the mixing ratio of a plurality of solvents to change the polarity of an eluent.
In column chromatography on vinyl alcohol copolymer (hereinafter may be referred to as "polymer column"), separation and purification are conducted by making good use of differences between components in absorption coefficient to the carrier and rate passing through solid support pores.
Therefore, when the a crude product mixture comprises a plenty of components, or a crude product mixture contains components having similar physical properties (adsorption coefficient, partition coefficient, etc.) to those of a component intended to purify, sufficient separation and purification can not be fully achieved unless the mixing ratio of an eluent is gradually changed. Accordingly, combinations of solvents mixable freely in any ratio have heretofore been selected.
For example, in Japanese Patent Publication No. 44316/1990, is disclosed a separation and purification process in which crude lecithin is caused to be adsorbed on a silica gel column, and a lower alkanol having 1-4 carbon atoms and containing water in an amount up to 20 vol % is then used.
Besides, Japanese Patent Application Laid-Open (KOKAI) No. 277457/1989 discloses a process in which crude lecithin is caused to be adsorbed on a silica gel column, and then separated and purified with a mixed solvent system of ethanol/water/n-hexane.
Further, Japanese Patent Application Laid-Open (KOKAI) No. 145189/1986 discloses a process in which crude lecithin is caused to be adsorbed on a silica gel column, and then separated and purified with a mixture of petroleum ether having a boiling point of 40.degree.-80.degree. C., a lower alkanol having 1-4 carbon atoms and water.
Many materials such as silica gel, alumina, diatomaceous earth, polymer beads and ion-exchange resins ape used as solid supports for column chromatography. However, diatomaceous earth is not said to be sufficient in separative power as a solid support for chromatography. Besides, the ion-exchange resins are expensive and have a restriction that a substance to be separated and purified must be ionic. Therefore, silica gel and alumina are generally often used from the overall industrial viewpoint including separation efficiency, operation efficiency and economical efficiency.
Alumina has a merit that when it is subjected to an acid or basic treatment, components making up a crude product mixture can be separated making good use of a difference in pH between the components. However, it involves drawbacks that its adsorptivity is too strong to completely elute the intended individual components, and depending upon the kinds of components, alumina itself of a solid support acts as a catalyst to hydrolyze some components with water contained in the solid support and/or solvents, resulting in reduction in the purity of the components during the separation. Therefore, alumina can not be applies to the separation and purification of all crude products.
On the other hand, the separation and purification method by the silica gel column has an advantage that the intended components can be reliably separated. However, even if an effluent is concentrated to recover solvents, they can not be reused because the mixing ratio of the solvents is not maintained constant. Therefore, the solvents are used only once and then thrown. Further, when a water/alcohol system is used as a mobile phase as disclosed in Japanese Patent Publication No. 44316/1990 and Japanese Patent Application Laid-Open (KOKAI) No. 277457/1989, the silica gel of a solid support is deteriorated to a particularly marked extent. A column constructed can not hence be reused.
There is therefore a demand for development of a method which can improve the above-described drawbacks involved in the conventional purification methods or processes by column chromatography, and makes it possible to make effective use of resources and also can more enhance economical efficiency while retaining separation efficiency to an extent equal to or higher than the conventional methods.
With a view toward reusing solvents for separation and reducing production cost from the above-described background, it has been attempted to rectify recovered solvents to collect a specific solvent. However, immense energy is required to operate a rectifier, and moreover many solvent systems form azeotropic mixtures, so that the purity of the specific solvent can not be raised higher than a fixed level by the rectification alone. Therefore, in most cases, economical efficiency is rather deteriorated on the contrary. In addition, there is a drawback that when water is used in an eluent, a solid support such as silica gel is remarkably deteriorated to become unfit for reuse.